A rider propelled vehicle is generally understood to be typically a two wheeled vehicle with a front free rolling, steerable wheel and a rear free rolling, non-steerable wheel, connected to each other by a frame including a rider platform positioned between the wheels on which the rider can support himself. To move, the rider can actuate pedal to provide rotational force on the rear wheel producing locomotion. This locomotion process has been employed for bicycles for quite some time as shown in U.S. Pat. No. 540,977 issued on Jun. 11, 1895.
The limitation to the initial bicycle design was that the pedals were connected to the drive wheel either directly or by a chain. However, this connection was typically a single gear connection. Attempting to improve the efficiency of the connection includes the advent of the sprocket nest and derailleur system as shown in U.S. Pat. No. 3,535,950 issued on Oct. 27, 1970. In the reference, the derailleur is disposed at or near the rear sprocket nest.
The derailleur system currently used in bicycles has been engineered to allow the chain to smoothly move to an adjacent sprocket within the sprocket nest at selected locations around each sprocket. Each sprocket is modified to provide clearance for chain shifting with a small plurality of reduced sized chain pickup teeth with modified shape at selected locations on the sprocket, but with adjacent normally sized teeth providing adequate chain grip and strength around the rest of the sprocket's outer periphery or circumference.
The chain travel is directed by a movement of the derailleur guiding the chain from the sprocket it is on and feeding the chain onto an adjacent larger sprocket when decreasing the speed or a smaller sprocket when increasing the speed.
The bicycle derailleur devices are physically mounted on the frame of the bicycle and its movement is generally operated by a guide wire or cable extending from a shifting lever attached on the handle bar to the derailleur. When the rider selects a new sprocket, he moves the lever moving the wire or cable which in turn repositions the derailleur to effect a sprocket change. The derailleur is a sophisticated device that has a fixed structure attached to the frame or rear axle and a movable structure that is held in position by at least one double pivot with multiple heavy duty springs that allow the movable elements to rotate or move in the path of a parallelogram created by two opposing plates hinged to move parallel relative to the other. This movement enables the chain guide portion of the derailleur to move relative to the sprocket nest in a relatively uniform path in relation to the guide and the sprockets while minimizing twisting the chain.
In order to function properly, the chain slack that exists when the chain is on the sprocket must be taken up. The amount of chain slack is reduced as the chain moves to larger sprockets. In bicycles, the derailleur chain guide system is positioned to extend well below the axle and frame. This enables the chain to serpentine through the low hanging derailleur guide system by having the chain extend well below the largest of the sprockets. Due to this limitation, derailleurs are not available for vehicle such as scooters which include much smaller wheels and tire and therefore have insufficient clearance for the typical derailleur.
Recently, a new generation of scooters and bicycles has been developed with reciprocating foot pedals such as U.S. Pat. No. 8,128,111. These vehicles, particularly the scooters, have frames that have a very low center of gravity to make the vehicles more stable. The frames are so low to the ground that the prior art derailleurs conventionally positioned below the rear sprocket nest are virtually useless. Nevertheless, these vehicles need a shifting device to allow the rider to selectively change speeds. Further, positioning the derailleur adjacent to the rear sprocket nest is not advantageous for such a vehicle as a scooter. It would be preferred to have a derailleur that is disposed between the front and rear sprocket nests.
Further, the typical derailleur can only actuate one sprocket nest at a time. As such, for a vehicle such as a bicycle with a sprocket nest at the rear wheel and a sprocket nest at the pedal assembly, two derailleurs are required. Dual derailleurs are simply too bulky and complicated for today's' scooter. Further, placing the derailleur adjacent to the rear wheel requires that the pedal of a scooter such as shown in U.S. Pat. No. 8,128,111 be too high over the rear wheel axle or spaced too far apart to accommodate the traditional derailleur.
Further, the typical derailleur and drive assembly causes the chain to contact the sprocket only on about one half of the sprocket as shown in U.S. Pat. No. 6,572,500. As can be seen, the chain contacts the rear sprocket on about half of the teeth of the rear sprocket and only about half of the teeth of the front sprocket. This limits the diameters differential between sprockets in increasing size on the sprocket nest. If the differential is too large, the chain tends to skip or to even fall off the sprocket nest.
Therefore, it is the object of the present invention to provide for a derailleur that can be used with a low profile vehicle such as a scooter.
It is another object of the present invention to provide a derailleur that is disposed between a front and rear sprocket nest.
It is another object of the present invention to provide a derailleur that can be used to change sprockets for both the front and rear sprocket nest with the need for a dual derailleur system.
It is another object of the present invention to provide a derailleur that increases the contact surface between the chain and the sprockets of a sprocket nest.